CAPEC 23

An attack of this type exploits the host's trust in executing remote content including binary files. The files are poisoned with a malicious payload (targeting the file systems accessible by the target software) by the attacker and may be passed through standard channels such as via email, and standard web content like PDF and multimedia files. The attacker exploits known vulnerabilities or handling routines in the target processes. Vulnerabilities of this type have been found in a wide variety of commercial applications from Microsoft Office to Adobe Acrobat and Apple Safari web browser. When the attacker knows the standard handling routines and can identify vulnerabilities and entry points they can be exploited by otherwise seemingly normal content. Once the attack is executed, the attacker's program can access relative directories such as C:\Program Files or other standard system directories to launch further attacks. In a worst case scenario, these programs are combined with other propagation logic and work as a virus.

PHP is a very popular web server. When PHP is used with global variables, a vulnerability may be opened that affects the file system. A standard HTML form that allows for remote users to upload files, may also place those files in a public directory where the attacker can directly access and execute them through a browser. This vulnerability allows remote attackers to execute arbitrary code on the system, and can result in the attacker being able to erase intrusion evidence from system and application logs.

Reference - http://www.owasp.org/index.php/File_System